Browder discovered that the off-therapy period allows the blood cells that feed tumors to regenerate and continue to nourish the very cancer cells that chemotherapy seeks to destroy.

For example, a standard treatment schedule for a woman with breast cancer might be to blast the cancer cells with the maximum dose of chemotherapy drugs she can stand, then allow her to rest for three weeks while her body recuperates, Folkman said.

"Conventional philosophy is to try to kill all the tumor cells early,"

Folkman said. "But you're forced to stop and rescue the bone marrow."

During the intensive drug treatment, cancer cells and surrounding tissue die off. But when the drugs are taken away for even a few weeks, endothelial cells can grow back.

In a statement issued March 31, Browder explained that unlike cancer cells, which tend to quickly divide and mutate, endothelial cells "are not themselves cancerous and thus are much less likely to develop resistance to chemotherapy."

In addition, giving lower doses of the standard drug proved "more effective and less toxic" in mice, the statement said.

Browder and Folkman's data point cancer researchers in a promising direction, especially because their evidence has been corroborated by other researchers who have conducted similar experiments.